Taeniasis/cysticercosis

Key facts

Taeniasis is acquired by humans through the ingestion of tapeworm larval cysts (cysticerci) in undercooked pork.

Human tapeworm carriers excrete tapeworm eggs in their faeces and contaminate the environment when they defecate in open areas.

Humans can also become infected with T. solium eggs by ingesting contaminated food or water (human cysticercosis) or as a result of poor hygiene.

Ingested eggs develop to larvae (called cysticerci) and migrate through the human body. When they enter the central nervous system they can cause neurological symptons (neurocysticercosis), including epileptic seizures.

T. solium is the cause of 30% of epilepsy cases in many endemic areas where people and roaming pigs live in close proximity.

More than 80% of the world’s 50 million people who are affected by epilepsy live in low and lower-middle income countries.

Taeniasis is an intestinal infection caused by 2 species of tapeworms. The most important human Taenia tapeworm infections are caused by Taenia solium (pork tapeworm) and Taenia saginata (beef tapeworm).

Humans can become infected with T. saginata when they consume beef which has not been adequately cooked, but Taeniasis due to T. saginata has no major impact on human health. Infection with T. solium occurs when humans eat raw or undercooked, infected pork, and this infection can result in devastating effects on human health. The main reason is that humans can also become infected with T. solium eggs by ingesting contaminated food or water (human cysticercosis) or as a result of poor hygiene. In this case, tapeworm larvae (cysticerci) develop in the muscles, skin, eyes and the central nervous system. When cysts develop in the brain, the condition is referred to as neurocysticercosis. Symptoms include severe headache, blindness, convulsions, and epileptic seizures, and can be fatal. Neurocysticercosis is the most frequent preventable cause of epilepsy worldwide, and is estimated to cause 30% of all epilepsy cases in in countries where the parasite is endemic.

Cysticercosis mainly affects the health and livelihoods of subsistence farming communities in developing countries of Africa, Asia and Latin America. It also reduces the market value of pigs and cattle, and makes pork unsafe to eat. In 2015, the WHO Foodborne Disease Burden Epidemiology Reference Group identified T. solium as a leading cause of deaths from food-borne diseases, resulting in a considerable total of 2.8 million disability-adjusted life-years (DALYs).

T. solium cysticercosis was added by WHO to the list of major neglected tropical diseases in 2010.

Transmission

Taeniasis is acquired by humans through the inadvertent ingestion of their cysticerci in undercooked pork or beef. Once in the human body, cysticerci develop into adult tapeworms that live in the intestine and release egg-bearing gravid proglottids (segments) which are passed with faeces.

Cysticercosis is acquired when proglottids or eggs are ingested and developing larvae migrate through the body and form cysts in tissues. This is the case in pigs and cattle but, in the case of T. solium, it can also affect humans, usually when they swallow T. solium egg-contaminated soil, water or food (mainly vegetables). When the central nervous system is affected, the infection is called neurocysticercosis.

Taeniasis and (neuro)cysticercosis are common in areas where animal husbandry practices are such that pigs and cattle come into contact with human faeces.

Symptoms

Taeniasis due to T. solium or T. saginata is usually characterized by mild and non-specific symptoms. Abdominal pain, nausea, diarrhoea or constipation may arise when the tapeworms become fully developed in the intestine, 6–8 weeks after ingestion of meat containing cysticerci.

These symptoms may continue until the tapeworm dies following treatment, otherwise it may live for years.

In the case of cysticercosis due to T. solium, the incubation period is variable, and infected people may remain asymptomatic for years.

In some endemic regions (particularly in Asia), infected people may develop visible or palpable nodules (a small solid bump or node that can be detected by touch) beneath the skin (subcutaneous). Neurocysticercosis is associated with a variety of signs and symptoms depending on the number, size, stage, and location of the pathological changes as well as the host’s immune response and the parasite’s genotype, but can also be clinically asymptomatic. Symptoms may include chronic headaches, blindness, seizures (epilepsy if they are recurrent), hydrocephalus, meningitis, dementia, and symptoms caused by lesions occupying spaces of the central nervous system.

Treatment

Taenaisis can be treated with praziquantel (5–10 mg/kg, single-administration) or niclosamide (adults and children over 6 years: 2 g, single-administration after a light meal followed after 2 hours by a laxative; children aged 2–6 years: 1 g; children under 2 years: 500 mg).

Currently there are no standard treatment guidelines for neurocysticercosis and treatment has to be tailored to the individual case. Since the destruction of cysts may lead to an inflammatory response, treatment of active disease may include long courses with praziquantel and/or albendazole, as well as supporting therapy with corticosteroids and/or anti-epileptic drugs, and possibly surgery. The dosage and the duration of treatment can vary greatly and depend mainly on the number, size, location and developmental stage of the cysts, their surrounding inflammatory edema, acuteness and severity of clinical symptoms or signs.

Prevention and control

To prevent, control and possibly eliminate T. solium, proper public health interventions with an approach spanning veterinary, human health and environmental sectors are required. Eight interventions for the control of T. solium can be used in different combinations designed on the basis of the context in the countries:

access to preventive chemotherapy

identification and treatment of taeniasis cases

health education

improved sanitation

improved pig husbandry

anthelmintic treatment of pigs

vaccination of pigs

improved meat inspection, and processing of meat products.

Reliable epidemiological data on geographical distribution of T. solium taeniasis/cysticercosis in people and pigs is still scarce.

Appropriate surveillance mechanisms should enable new cases of human or porcine cysticercosis to be recorded in order to help identify communities at high risk and focus prevention and control measures in these areas.

WHO’s role

Working with the veterinary and food safety authorities as well as with other sectors will be essential to attain the long-term outcomes of reducing the burden of disease and safeguarding the food value chain. WHO Neglected Tropical Diseases (NTDs) team is working closely with other WHO departments in the areas of mental health, research and development, food safety, water, and sanitation, as well as partner agencies such as the Food and Agriculture Organization of the United Nations (FAO) and the World Organization for Animal Health (OIE) to meet the needs for interdisciplinary collaboration to control T. solium, with the final goal to prevent human suffering due to neurocysticercosis.

WHO has, with countries and key partners, taken the first steps towards identifying the “best-fit” strategy to interrupt transmission of T. solium and improve case detection and management of neurocysticercosis using the tools currently available.

Several countries are mounting pilot programmes with the available tools while conducting operational research to measure impact and refine strategies. More countries are interested in joining the WHO network for the control of taeniasis/cysticercosis.

Improved, simple, cost-effective and rapid diagnostic tools are still needed for use in field conditions to detect T. solium carriers as well as human and porcine cysticercosis cases, and to direct programme planning and monitoring. In December 2015, a Stakeholder Meeting on T. solium Taeniasis/Cysticercosis diagnostic tools was held in WHO headquarters to address the lack of a suitable diagnostic toolbox for Taeniasis, Cysticercosis and Neurocysticercosis (NCC) for patient care and surveillance purposes in low resource settings.